Revealed: How US and UK spy agencies defeat internet privacy and security

• NSA and GCHQ unlock encryption used to protect emails, banking and medical records • $250m-a-year US program works covertly with tech companies to insert weaknesses into products • Security experts say programs 'undermine the fabric of the internet'

US and British intelligence agencies have successfully cracked much of the online encryption relied upon by hundreds of millions of people to protect the privacy of their personal data, online transactions and emails, according to top-secret documents revealed by former contractor Edward Snowden.

The files show that the National Security Agency and its UK counterpart GCHQ have broadly compromised the guarantees that internet companies have given consumers to reassure them that their communications, online banking and medical records would be indecipherable to criminals or governments.The agencies, the documents reveal, have adopted a battery of methods in their systematic and ongoing assault on what they see as one of the biggest threats to their ability to access huge swathes of internet traffic – "the use of ubiquitous encryption across the internet".Those methods include covert measures to ensure NSA control over setting of international encryption standards, the use of supercomputers to break encryption with "brute force", and – the most closely guarded secret of all – collaboration with technology companies and internet service providers themselves.Through these covert partnerships, the agencies have inserted secret vulnerabilities – known as backdoors or trapdoors – into commercial encryption software.The files, from both the NSA and GCHQ, were obtained by the Guardian, and the details are being published today in partnership with the New York Times and ProPublica. They reveal:• A 10-year NSA program against encryption technologies made a breakthrough in 2010 which made "vast amounts" of data collected through internet cable taps newly "exploitable".• The NSA spends $250m a year on a program which, among other goals, works with technology companies to "covertly influence" their product designs.• The secrecy of their capabilities against encryption is closely guarded, with analysts warned: "Do not ask about or speculate on sources or methods."• The NSA describes strong decryption programs as the "price of admission for the US to maintain unrestricted access to and use of cyberspace".• A GCHQ team has been working to develop ways into encrypted traffic on the "big four" service providers, named as Hotmail, Google, Yahoo and Facebook.